Abstract

Sulfate attack on concrete is one of the well-known phenomena that lead to deterioration of concrete structures. Conventionally, sulfate attack is believed as arising from two major sulfate reactions: a) the sulfate ions react with 3CaO center dot Al2O3 and its hydration products to form ettringite; and b) the sulfate ions react with calcium hydroxide to form gypsum. Both reactions increase in volume, resulting in expansion and subsequent cracking of the concrete. A different form of sulfate attack, which is not well known by Chinese engineers, has been extensively reported and investigated in recent years - thaumasite form of sulfate attack. Different from the conventional sulfate attack, sulfate ions react with calcium silicate hydrate, the main phase of Portland cement hydration, to form thaumasite. Thus, TSA completely destroys the cementitious binding ability of the concrete by transforming it into a mush. This paper introduces the background of TSA, its risk factors, formation conditions, reaction mechanism and recent UK guidance on reducing its risk on concrete structures.